The Transient Behavior of a Low Power Laboratory Xenon Hall Thruster

Characterization of the transient behavior of a co-axial xenon Hall accelerator is presented. Electrostatic probes, including floating, grounded, emissive (plasma potential), and swept Langmuir probes, are used to measure the time-average and spectral properties of the plasma both outside and within the acceleration channel. The measurements confirm the existence of low-frequency (< 100kHz) coherent azimuthal drift waves and more stochastic (turbulent) disturbances within the channel. The properties of these disturbances depend on the location within the channel, and where in the current-voltage characteristics the thruster is operating, in agreement with observations in other Hall thrusters documented in the literature. Measurements of the time-average plasma potential indicates that in this particular Hall thruster, the largest axial electric field exists between the channel exit and cathode plane, consistent with recent laser-induced fluorescence measurements in the same device, and coincident with the region of the thruster where there is a negative gradient in the magnetic field. The average azimuthal wave speeds are measured and compared to the E X B drift velocity. The electron temperature is fairly uniform along the discharge, and in the range of 5-10 eV, in qualitative agreement with the observed potential differences between the floating potential and floating emissive probes.